In recent years, liquid crystal display devices are rapidly becoming popular as alternatives to cathode-ray tubes (CRTs). Such liquid crystal display devices are used in a wide variety of devices, such as television sets, monitors, and mobile phones, because of their characteristics such as energy saving, low-profile, and lightweight.
The liquid crystal display device most commonly used in the past is a TN (Twisted Nematic) mode liquid crystal display device that uses liquid crystal molecules having a positive dielectric anisotropy.
The TN mode liquid crystal display device has wide production margin and excellent productivity; however, the TN mode liquid crystal display device has the problem that a contrast ratio greatly lowers when a display surface of the liquid crystal display device is viewed from directions other than the front, for example, when it is viewed at oblique angles from above, from underneath, from the left side, and from the right side. More specifically, the TN mode liquid crystal display device has the problem that when the display surface is viewed from the front, multiple levels of grayscale from black to white can be clearly observed, but when the display surface is viewed at oblique angles from above, from underneath, from the left side, and from the right side, difference in luminance between the levels of grayscale becomes very unclear. In addition, the TN mode liquid crystal display device has the problem of the so-called grayscale inversion phenomenon that a darker part when the display surface is viewed from the front appears to be brighter when the display surface is viewed at oblique angles from above, from underneath, from the left side, and from the right side.
As described above, the TN mode liquid crystal display device has the problem that its image quality is significantly deteriorated when the liquid crystal display device is viewed at oblique angles from above, from underneath, from the left side, and from the right side, as compared with when viewed from the front.
Hence, the TN mode liquid crystal display device has high dependence of image quality on viewing angles, and is therefore not suitable for an application in which the liquid crystal display device is expected to be viewed from a direction other than the front.
Known as liquid crystal display devices in which such viewing angle dependence of image quality is improved are an IPS (In-Plane Switching) mode liquid crystal display device, an MVA (Multi-domain Vertical Alignment) mode liquid crystal display device, an ASM (Axially Symmetric Aligned Micro-cell) mode liquid crystal display device, etc.
Each of the liquid crystal display devices (liquid crystal display devices in wide viewing angle mode) with improved viewing angle dependence of image quality alleviates the above-described problems, i.e. the decrease in contrast ratio and the grayscale inversion, that can occur when the display surface of the liquid crystal display device is viewed at the oblique angles, to some extent. However, the viewing angle dependence of the γ characteristics, which shows a relation between display luminance and grayscale, is not still improved.
Such a viewing angle dependence of the γ characteristics is more prominent in the MVA mode liquid crystal display device and the ASM mode liquid crystal display device, than in the IPS mode liquid crystal display device.
Generally, γ characteristics of a liquid crystal display device is optimized with reference to γ characteristics obtained when the display surface of the liquid crystal display device is viewed from the front. However, when the γ characteristics has viewing angle dependence, a shift occurs between the γ characteristics obtained when the display surface is viewed at the oblique angles and the γ characteristic optimized when viewed from the front.
The amount of shift is not so great and is not a problem in the vicinities of a region showing the highest display luminance and a region showing the lowest display luminance. However, in a region showing halftones, display luminance obtained when viewed at the oblique angles is considerably higher than that obtained when viewed from the front. This results in deterioration in image quality, such as excess brightness, when the display surface is viewed at the oblique angles.
In view of this, as shown in FIG. 14, there has been proposed a liquid crystal display device employing a multi-picture element drive method (area coverage modulation), with an improved viewing angle dependence of γ characteristics, wherein picture elements are driven in such a manner that an average luminance of two sub-picture elements which constitute one picture element becomes a target luminance of the one picture element.
In the liquid crystal display device employing a multi-picture element drive method, the two sub-picture elements are allowed to provide display of high luminance level and display of low luminance level, respectively, both of which cause small variations in display luminance depending upon viewing angles, so that display of a halftone is provided by averaging luminance levels of these two sub-picture elements. Thus, it is possible to achieve a liquid crystal display device with an improved viewing angle dependence of the γ characteristics.
The following will describe a schematic configuration of an example of a conventional liquid crystal display device employing multi-picture element drive method, with reference to FIG. 14.
As shown in FIG. 14, one picture element 100 is composed of two separate sub-picture elements 101a and 101b. The sub-picture element 101a is connected to a scanning line Gn and a signal line Sm via a TFT (Thin Film Transistor) 102a. Further, the sub-picture element 101b is connected to the scanning line Gn and the signal line Sm via a TFT 102b. 
That is, gate electrodes of the TFTs 102a and 102b are connected to the common scanning line Gn, whereas source electrodes of the TFTs 102a and 102b are connected to the common signal line Sm.
Further, the sub-picture element 101a has a liquid crystal capacitor and an auxiliary capacitor. The liquid crystal capacitor is made up of a sub-picture element electrode 103a, a liquid crystal layer (not shown), and a counter electrode (not shown). The auxiliary capacitor is made up of (i) an auxiliary capacitor electrode 104a electrically connected to the sub-picture element electrode 103a, (ii) an insulating layer 105a, and (iii) an auxiliary-capacitor counter electrode 107a electrically connected to an auxiliary capacitor line 106a. 
On the other hand, as is the case with the sub-picture element 101a, the sub-picture element 101b has a liquid crystal capacitor and an auxiliary capacitor. The liquid crystal capacitor is made up of a sub-picture element electrode 103b, a liquid crystal layer (not shown), and a counter electrode (not shown). The auxiliary capacitor is made up of (i) an auxiliary capacitor electrode 104b electrically connected to the sub-picture element electrode 103b, (ii) an insulating layer 105b, and (iii) an auxiliary-capacitor counter electrode 107b electrically connected to an auxiliary capacitor line 106b. 
In the above-configured liquid crystal display device employing a multi-picture element drive method, after writing to the separate sub-picture elements 101a and 101b is completed and the TFTs 102a and 102b are turned off, voltages on the auxiliary capacitor lines 106a and 106b are changed to mutually different voltages. This allows the sub-picture elements 101a and 101b to practically hold different voltages.
FIG. 15 is a diagram schematically showing an equivalent circuit of a liquid crystal display device having a multi-picture element structure shown in FIG. 14.
As shown in FIG. 15, the auxiliary capacitor lines 106a and 106b are electrically connected respectively to two auxiliary capacitor trunk lines 108 and 109, which are electrically independent from each other. Applied to the auxiliary capacitor trunk lines 108 and 109, respectively, are vibration voltages being substantially identical in amplitude and vibration period with each other and being about 180° out of phase with each other.
Accordingly, the vibration voltages of mutually reversed phases are applied to the auxiliary capacitor lines 106a and 106b, respectively. This allows the sub-picture elements 101a and 101b to provide mutually different luminance levels (levels of grayscale), i.e. display of a bright luminance level and display of a dark luminance level both of which cause small variations in display luminance depending upon viewing angles. With an average luminance of the luminance levels of these sub-picture elements 101a and 101b, display of a halftone can be provided. Therefore, it is possible to achieve a liquid crystal display device having an improved viewing angle dependence of γ characteristics.
However, in a large liquid crystal display device employing a multi-picture element drive method in which auxiliary capacitor trunk lines 108 and 109 and auxiliary capacitor lines 106a and 106b have high load capacitances and high resistances, a high-definition liquid crystal display device, with a short horizontal scanning period, employing a multi-picture element drive method, a high-speed drive liquid crystal display device, with a short vertical scanning period and a short horizontal scanning period, employing a multi-picture element drive method, and the like liquid crystal display devices, luminance unevenness occurs due to adverse effects of delays and waveform distortions of auxiliary capacitor driving signals (vibration voltages) applied to the auxiliary capacitor trunk lines 108 and 109.
In order to prevent such luminance unevenness, it is necessary to reduce load capacitances and resistances of the auxiliary capacitor trunk lines 108 and 109 and the auxiliary capacitor lines 106a and 106b. By providing sufficiently broad line widths of the auxiliary capacitor trunk lines 108 and 109 and the auxiliary capacitor lines 106a and 106b, it is possible to prevent the luminance unevenness.
However, the liquid crystal display device having the configuration described above causes increase of an area in which the auxiliary capacitor trunk lines 108 and 109 and the auxiliary capacitor lines 106a and 106b are formed. This results in increase in area of a picture frame region as a non-display region in the liquid crystal display device, and decrease in aperture ratio. Therefore, the liquid crystal display device having the configuration described above is not preferred.
Alternatively, in order to reduce such luminance unevenness, vibration periods of the auxiliary-capacitor driving signals to be applied to the auxiliary capacitor trunk lines 108 and 109 can be lengthened. This makes it possible to prevent the influence of waveform distortions, thus reducing the luminance unevenness.
However, in order to carry out auxiliary capacitor driving that allows two sub-picture elements 101a and 101b connected to the respective scanning lines to hold different voltages, such an arrangement is accompanied by increase in type of required auxiliary capacitor driving signals and increase in number of auxiliary capacitor trunk lines. Further, one method for accelerating the rise of a signal when a delay is significant is to employ signal pre-emphasis driving. This, however, requires the auxiliary capacitor driving signal to be a voltage of four levels of amplitude although the auxiliary capacitor driving signal is generally a voltage of two levels of amplitude.
Therefore, the above-described approach to preventing luminance unevenness requires increase in number of auxiliary capacitor trunk lines and requires a large number of voltage sources for producing a variety of auxiliary capacitor driving signals, resulting in increase of a picture frame region of the liquid crystal display device and increase of a control board (external circuit board) provided outside the liquid crystal display panel. Thus, the above-described approach to preventing luminance unevenness is not preferred.
As described above, in the liquid crystal display device employing a multi-picture element drive method, it is difficult to narrow the picture frame region as a non-display region and the external circuit board. Therefore, an attempt to narrow such a non-display region has been made.
For example, Patent Literature 1 describes the configuration by which auxiliary capacitor driving signals are supplied to auxiliary capacitor lines via buffers capable of shaping waveforms of the auxiliary capacitor driving signals.
FIG. 16 is a view showing a schematic configuration of a liquid crystal display device configured to supply the auxiliary capacitor driving signals to the auxiliary capacitor lines via the buffers.
In the configuration of a liquid crystal display panel 140 shown in FIG. 16, the structure of display picture elements 141 each of which is composed of a plurality of sub-picture elements 142 and 143, and connections of sub-picture elements 142 and 143 and TFTs 144 and 145 with scanning lines Gn and signal lines Sm are the same as those previously described with reference to FIG. 14, and descriptions thereof are therefore omitted.
In the liquid crystal display panel 140 shown in FIG. 16, auxiliary capacitor driving signals, gate driver control signals (scan start signal and driving clock signal) upon which scanning line driving signals are based, and various kinds of power supply voltages are supplied from the controller 148 to the gate driver 151A.
To the gate driver 151A, auxiliary capacitor driving signals are inputted from terminals “CSVtypeA1R” through “CSVtypeA4R” of a terminal group C1. Further, the gate driver control signals are inputted from terminals “GSPOI” and “GCKOI” of the terminal group C1 in the gate driver 151A, and the power supply voltages are inputted from terminals “VGL”, “VGH”, “GND”, “VCC”, “VCSL”, and “VCSH” of the terminal group C1 in the gate driver 151A.
As shown in FIG. 16, the terminal groups C1 and C2 are provided at both ends of a terminal section 133 in a tape 131 of the gate driver 151A, and the terminals having the same terminal names in the terminal groups C1 and C2 are connected to each other. Further, the terminals “CSVtypeA1R” through “CSVtypeA4R” provided in the terminal group C1 are connected to the terminals “CSVtypeA1L” through “CSVtypeA4L” provided in the terminal group C2.
Therefore, the terminals “CSVtypeA1L” through “CSVtypeA4L” provided in the terminal group C2 of the gate driver 151A are connected respectively to terminals “CSVtypeA1R” through “CSVtypeA4R” provided in the terminal group C1 of a gate driver 151B having the same configuration as that of the gate driver 151A, via lines provided on a glass substrate 149. This allows the liquid crystal display panel 140 to have such an configuration that the auxiliary capacitor driving signals, the gate driver control signals, and the various kinds of power supply voltages, all of which are inputted to the gate driver 151A, can be supplied from the gate driver 151A to the gate driver 151B.
In addition, in the liquid crystal display panel 140, the gate driver 151A produces scanning line driving signals by using the incoming signals from the controller 148 upon which the scanning line driving signals are based, and then provide the scanning line driving signals to the scanning lines Gn connected to the terminals “OG1” through “OG272” of the gate driver 151A.
Meanwhile, the incoming auxiliary capacitor driving signals from the controller 148 subjected to waveform shaping in the buffers 121A and 121B provided in an integrated circuit 132 of the gate driver 151A, and then outputted from the terminals “CSVtypeA1″R” through “CSVtypeA4′R” and “CSVtypeA1′L through “CSVtypeA4′L”. Note that the terminals “CSVtypeA1′R” through “CSVtypeA4′R” and “CSVtypeA1′L” through “CSVtypeA4′L” are connected to auxiliary capacitor trunk lines 150 in the liquid crystal display panel 140.
Further, the auxiliary capacitor trunk lines 150 are connected to the auxiliary capacitor lines 151, and the auxiliary capacitor driving signals with reduced waveform distortions to be outputted from the buffers 121A and 121B to the terminals “CSVtypeA1′R.” through “CSVtypeA4′R.” and “CSVtypeA1′R” through “CSVtypeA4L” can be provided to all of the auxiliary capacitor lines 151 via the auxiliary capacitor trunk lines 150 connected to the terminals “CSVtypeA1′R” through “CSVtypeA4′R.” and “CSVtypeA1′L” through “CSVtypeA4′L”. This realizes the configuration that allows the sub-picture elements 142 and 143 to provide display of mutually different luminance levels.
According to the above configuration, the auxiliary capacitor driving signals are supplied via the buffers to the auxiliary capacitor lines 151. This makes it possible to enhance a driving ability of the auxiliary capacitors. Therefore, even when line widths of the auxiliary capacitor trunk lines 150 are narrow, it is possible to prevent the occurrence of luminance unevenness caused by waveform distortions or for other reasons.
Further, such a configuration eliminates the need for making vibration periods of the auxiliary capacitor driving signals longer than those in the conventional configuration, and thus eliminates the need for increasing the type of auxiliary capacitor driving signals.
Thus, Patent Literature 1 described that the liquid crystal display device disclosed therein enables narrowing of a picture frame region as a non-display region and an external circuit board.